Piston



Aug. 28, 1962 J. o. McLEAN ETAL 3,051,536

PISTON 2 Sheets-Sheet 1 Filed July 7, 1960 FIG. 7

FIG. 6

Ill i FIG. 3

INVENTORS JOHN 0. MC LEAN THOMAS L.FRITZLEN BY ROGER H. HEMJRICK v I8 22 FIG. 5

FIG. .4

THEIR ATTO RNEYS Aug. 28, 1962 J. o. MCLEAN ETAL 3,

PISTON 2 Sheets-Sheet 2 Filed July '7, 1960 FIG. #2

IN VEN TORS JOHN 0. MC LEAN FIG 8 THOMAS L. FRITZLEN BY ROGER H. HENDRICK FIG. 13

$2M LIP, %(LC.AM)

HEILAIT NEXS 3,53,53d Patented Aug. 28, 1962 3,051,536 PESTON John O. McLean, Thomas L. Fritzlen, and Roger H. Hendrick, Henrico County, Va, assignors to Reynolds Metals Company, Richmond, Va, a corporation oi Delaware Filed July 7, i960, Ser. No. 41,387 3 Claims. (Ci. 389-14) This invention relates to an improved piston for an internal combustion engine and particularly to such a piston having an aluminum alloy body and wear-resistant, semi-porous inserts in the thrust and anti-thrust areas of the piston skirt. The piston is adapted to be used in engines having aluminum alloy cylinder walls.

One of the difliculties experienced in using aluminum alloy pistons within an aluminum alloy cylinder wall has been the excessive wear of the aluminum alloys on each other. This occurs because, relatively speaking, aluminum is one of the softer metals and when it is in contact with itself at elevated temperatures it virtually welds to itself and results in excessive wear on the reciprocating pistons. The problem of scoring and scuffing of aluminum alloy pistons used within aluminum alloy cylinder walls has been overcome in many commercially accepted engines by inserting cast iron or like cylinder wall liners in the aluminum block. However, this solution of the problem is complicated and ineflicient in operation, and for many years an extensive search has ben conducted for a practical and economical means for producing an engine, particularly of the type used in conventional automobiles, having aluminum alloy pistons operating successfully over a standard service life in a cast aluminum alloy block having cylinder walls of the same or of a similiar alloy, unlined and uncoated.

A second problem apart from the excessive wear of aluminum on aluminum has been the scuffing and wear imparted to the skirt of the piston caused by cold-starting at -20 degrees Fahrenheit, which is a requirement in some areas of the United States and other countries. The insertion of special cylinder liners is undesirable, for reasons of cost as pointed out above, and it is not practicable to plate or spray the cylinder walls because of the technical problems of working inside such small spaces or because of the cost of the plating itself.

The present invention overcomes these difiiculties by providing a semi-porous, arcuate, wear-resistant metallic insert at the location of the thrust and anti-thrust positions on the skirt of the piston itself. Difliculty has previously been experienced when such inserts were attempted to be used in that the insert became loose because of the severe inertia loads encountered during normal operation. In accordance with the present invention, the piston skirt is provided with means for preventing the insert from loosening and moving longitudinally with the piston.

In one embodiment of the invention, the aluminum alloy piston is cast around the insert which is provided with inwardly flared longitudinal edges to lock the inserts in place. These inwardly flared longitudinal edges have a plurality of apertures throughout their length into which molten metal flows as the piston is cast thereby locking the inserts securely in place.

In another embodiment of the invention, mechanical fastening means are provided which pass through the individual inserts to hold them in place. In each of the foregoing embodiments, the skirt area of the piston is provided with stepped shoulders which prevent the insert from moving longitudinally with respect to the piston.

In the previously described structures, a superior piston assembly is obtained and the inserts are securely retained relative to the piston skirt under conditions that would otherwise loosen a conventional insert thereby acusing failure of the piston. It is within the purview of the present invention to bond the inserts adhesively to the piston skirt in addition to the mechanical fastening means to etiect maximum strength and rigidity for the piston assembly.

The foregoing advantages and objects of the present invention will become apparent in the course of the following description and appended claims, reference being had to the accompanying drawings which form a part of this specification and which are as follows:

FIG. 1 is a plan view of a piston formed in accordance with one embodiment of the invention;

FIG. 2 is a front elevational view partially in section of the piston of FIG. 1;

FIG. 3 is a fragmentary cross sectional view taken along the line 33 of FIG. 2;

FIG. 4 is a plan view of an insert for the piston of FIG. 1;

FIG. 5 is an end view of the insert shown in FIG. 4;

FIG. 6 is an end view similar to FIG. 3 showing a modified fragmentary end view;

FIG. 7 is a front elevational view of a piston formed in accordance with miother embodiment of the invention;

FIG. 8 is a fragmentary cross sectional view taken along the line 8-8 of HG. 7;

FIG. 9 is a cross sectional view taken along the line 99 of FIG. 7;

FIG. 10 is a plan view of an insert for the piston of FIG. 7;

FIG. 11 is an end elevation of the insert shown in FIG. 10;

FIG. 12 is a fragmentary view showing the apparatus in one end of the insert shown in FIG. 11; and

FIG. 13 is a fragmentary end view similar to FIG. 8 showing a modified piston.

Referring now more particularly to FIGURES 1-5 of the drawings, there is shown a piston indicated generally at it? having a ring area, designated generally by the numeral 12, and a cylindrical skirt 14. The skirt 14 is provided with diametrically opposed wrist pin supporting bosses 16.

The piston it? has been cam ground to an oval shape in accordance with conventional practice. This provides a pair of diametrically opposed wear areas, also referred to as thrust and anti-thrust areas, located substantially normal to the axis of the wrist pin sup-porting bosses 16. The cylindrical skirt 14 is provided with. a recess in each of these opposed wear areas in which are received wearresistant metallic inserts 18. These inserts 18 are made from a semi-porous ferrous material such as cast iron or cold rolled steel and are held in place by rivets 20 passing through holes 22 and countersunk in inserts 18.

FIGURE 5 illustrates the arcuate cross section for the ferrous metal inserts 18. Although cast iron has a coefiicient of thermal expansion which is materially different from that of aluminum, the inserts 18 are made so thin, such as of an inch, that the piston as a whole has a coefiicient of expansion substantially the same as aluminum so that the piston is compatible with a high silicon alloy cylinder. For example, the coeflicient of thermal expansion for a typical aluminum alloy is about 13 X 10- inches per inch per degree Fahrenheit and only about 6.6 l0 inches per inch per degree Fahrenheit for cast iron. However, because the insert is extremely thin, the composite piston expands and contracts at substantially the same rate as the aluminum alloy cylinder.

The particular aluminum alloy of which the piston it is made, including the skirt 14, is not critical for purposes of the invention. Piston alloys conventionally have silicon as the principal minor alloying element, in

relatively high proportions, such as about 12 percent or more, but the amount or presence of silicon is not critical with respect to the present invention.

The inserts 18 are received within a recess defined partially by a horizontal shoulder 24 (FIG. 3) which prevents the inserts 13 from moving toward the ring area 12 during reciprocation of the piston.

Referring now to FIGURE 6, there is shown a modified piston wherein the recess in the thrust and antithrust areas is further defined by a lower horizontal shoulder 25 in addition to the horizontal shoulder 24- which further restrains the inserts 118. In addition to the use of one or more shoulders, the inserts 18 may be adhesively secured to the piston skirt.

Referring now to FIGURES 7-12, there is shown a preferred embodiment of the invention wherein a piston 10 having an annular ring area 12 and skirt 14 is cast about an insert indicated generally at 26. Piston 10 has diametrically opposed wrist pin supporting bosses 16 as in the previously described piston. Insert 26 is provided with an arcuate central portion 28 which conforms substantially to the curvature of piston skirt 14 and inwardly flared longitudinal edges 30 as best seen in FIGURES 9 and 10. Each of the inwardly flared longitudinal edges 30 is provided with a series of apertures 32 throughout the length of the edges into which apertures the molten metal from the piston flows during the casting operation. The insert 26 therefore is extremely secure and rigid with respect to the piston and will not become dislodged as the piston 26 is reciprocated under severe wear and inertia loads. As an added precaution, the metal is cast around insert 26 to provide a shoulder 29 to prevent the insert from moving toward the ring area 12.

FIGURE 13 discloses a modified piston in which the metal of the piston 10 is cast so as to produce both upper shoulder 29 and a lower shoulder 31 to insure that the insert will not become dislodged as the piston is reciprocated.

As in the example shown in FIGURES 1-6, the insert 26 is preferably made from cast iron or cold rolled steel which is semi-porous in nature and which is very thin so that the coefiicient or thermal expansion for the piston as a whole will be substantially the same as that for the aluminum alloy employed. Therefore, the pistons of the present invent-ion may be used in combination with an aluminum alloy cylinder wall without adverse effects which could be caused by substantial differences in thermal expansion.

It has been found by actual experimentation that on pistons for a Renault 4 CV automobile, 1956 model, having piston diameters of 2.146 inches and having been cam ground with a .011 cam, thereby producing a piston which is .011 inch out of round, that a wear area of about inch was obtained on the surface of the skirt 14. Inserts 18 for the embodiments shown in FIGURES 1-6 measuring 1 x 1 /8 x inches (1 7 x 1 /8 x ,3 inches for FIG. 6) were prepared with a surface finish of 25 micro-inches R.M.S., drilled and countersunk for rivets 20, and attached to the piston skirt 14. The width of these inserts of 1% inches provided a surface coverage about 20 percent greater than the actual wear area. The sector angle, designated on in FIG. 1, subtended by the insert 18 is about 60.

For the embodiments shown in FIGURES 7-13, the angle 13 (FIG. 9) subtended by the ends of the insert 26 is greater than the angle on shown in FIGURE 1 because of the presence of inwardly flared edges 30. However, the distance w (FIG. 7) is substantially the same as the arc subtended by the angle a in FIGURE 1. In other words, the wear area, and therefore the exposed area of the inserts, will be substantially the same for inserts used on the same size pistons. For the Renault 4 CV, 1956 model, having a piston diameter of 2.146 inches,

the angle p (FIG. 10) made between a line projecting from the outer surface of the flared edges 30 with a center line drawn to the center of curvature of arcuate portion 23 is 45. It will be appreciated that the specific angle ,0 will vary with different piston diameters, and that the essential feature is that the insert be provided with inwardly flared edges which will serve to lock the insert in place when the piston is cast around it.

The semi-porous metal of the cast iron or cold rolled steel insert is considered to be an important feature of the present invention. It has been found, for example, that cast iron retains enough residual lubricating oil to prevent scufiing and scoring during cold starts. Tests were performed to demonstrate the oil retention properties of the cast iron inserts of the present invention. Thus 3- x 3 x samples were prepared with a small hole .0625 inc-h) drilled near one corner for purposes of suspending the samples. The surface finish was ground to a 25 micro-inch R.M.S. finish. These surfaces were obtained by a grinder and checked on a proficorder.

In accordance with accepted analytical techniques, the samples were washed with hexane, dried at F., and weighed until a constant weight within plus or minus .3 mg. was obtained. Generally, four or five rinses with a stream of hexane from a wash bottle were sufficient to meet this standard. The samples were then immersed in Shell Rotella 20W oil at room temperature by suspending them from a wire for 30 minutes.

Each sample was then removed from the oil and allowed to drain for five minutes at room temperature. After this preliminary draining, each sample was placed in a 160 F. oven for four hours. The samples were suspended at a slight angle fro-m vertical with the corner of the square samples resting on absorbent filter paper.

Each sample was then removed from the oven and all edges of the sample were carefully wiped on both sides. The bottom corner which rested on the filter paper usually had a blob of oil on it which was wiped A inch from the corner to avoid inconsistent results because of different sized blobs. After wiping, each sample was weighed to the nearest tenth of a milligram. This weighing together with the initial weighing provide a measure of what may be referred to as the original oil retention.

Each sample was then washed three times with hexane as previously described with the amount remaining after three such washings considered to be that amount of oil which will be retained permanently. The weight of the oil retained is determined by subtracting the original weight of the sample from the weight of the sample after the heating, draining and wiping. This difference divided by the area of the sample ('both sides) gives an oil retention Value in milligrams per square inch. The weight of permanent oil retention, which is taken to be the oil remaining after the three washings, is found by subtracting the original weight of the samples from the weight after these three washings. It was found that cast iron had an original oil retention of 2.3 mg. per square inch and a permanent oil retention of .48 mg. per square inch which is about 21 percent permanent oil retention. 7

For purposes of comparison, Babbitt metal samples were prepared and tested as previously described and it was found that it had an original oil retention of 1.7 mg. per square inch and an oil retention after three washings with hexane of zero. That is to say, the Babbitt metal samples have no permanent oil retention compared with about 21 percent permanent oil retention for cast iron.

In order to demonstrate the invention further, the engine of a Renault 4 CV automobile, 1956 model, was torn down, and several of the cast iron cylinder sleeves were replaced with aluminum alloy cylinder sleeves (about 15 to 20 percent silicon). The aluminum pistons were duplicated with aluminum pistons of the same aluminum alloy (about 8.5 to 10.5 percent silicon) and identical construction. The test pistons were provided with chrome-plated steel piston rings of the same size and shape as the original rings. All critical dimensions were duplicated, as exactly as possible, in each of the replacement parts before they were installed. One set of pistons was prepared in accordance with each embodiment of the invention and installed in the aluminum alloy sleeves, and the rebuilt engine was installed in the automobile, which was driven 500 miles at 300 mph. to break in the pistons before the tests began.

The broken-in rebuilt engine was supplied with the standard amount of oil (-30 weight motor oil, Shell Oil Companys X-lOO Multi-Vis). A special oil pan was installed, with means for pumping refrigerant through it, and refrigerant was pumped through the oil pan and engine block until the whole engine had reached a temperature below 0 F. This temperature was maintained for a minimum of three hours at the beginning of each test cycle, and then the engine was started and idled for one minute. It has then driven on the road for ten minutes at 25 m.p.h., and the throttle was then opened wide for about minutes, which caused the automobile to run at about 65 to 70 m.p.h., and the oil temperature to reach about 180 F. The automobile was then stopped and allowed to stand idle at normal "temperature for about 3 /2 to 16 hours, which completed the first cycle of the cold-start test. This test cycle was repeated numerous times, and then the engine was torn down for inspection of parts. All of the pistons having the inserts as shown and described in the invention and the surrounding aluminum alloy cylinder walls were found to be in excellent condition, with no evidence of scufling, which refers to wide and deep destruction of the surface finish of the cylinder wall, and no significant scoring, which refers to narrow, shallow lines indented into the surface finish of the cylinder wall.

For purposes of comparison, a set of the same aluminum alloy pistons without inserts were similarly installed and run in the engine. These pistons showed excessive scuffing and scoring even before the first cold start was reached. That is, scufiing and scoring was pronounced during the break-in period. Similarly, sets of aluminum alloy pistons plated with chrome were installed and tested in the manner previously described. These pistons were found to scuff excessively during the cold-start test.

While present preferred embodiments of the invention have been illustrated and described, it will be understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims.

What is claimed is:

1. A cast piston for an internal combustion engine having an aluminum body with an annular ring area and a cylindrical skirt depending therefrom, said skirt having diametrically opposed wrist pin supporting bosses with aligned pin holes therein, said skirt having diametrically opposed wear areas substantially normal to the axis of said wrist pin bosses, said skirt having an exterior recessed portion in each of said wear areas, a semi-porous, arcuate, wear-resistant, metallic insert received within each of said recessed portions, said inserts being cast integrally with said piston and having their longitudinal edges flared inwardly throughout their entire length, and said inwardly flared longitudinal edges having a plurality of apertures throughout their length to receive metal from said piston as said piston is cast to lock said inserts in place.

2. A cast piston for an internal combustion engine having an aluminum body with an annular ring area and a cylindrical skirt depending therefrom, said skirt having diametrically opposed wrist pin supporting bosses with aligned pin holes therein, said skirt having diametrically opposed Wear areas substantially normal to the axis of said wrist pin bosses, said skirt having an exterior recessed portion in each of said wear areas, a semi-porous, arcuate, wear-resistant, metallic insert received Within each of said recessed portions, said inserts being cast integrally with said piston and having their longitudinal edges flared inwardly throughout their entire length, said inwardly flared longitudinal edges having a plurality of apertures throughout their length to receive metal from said piston as said piston is cast to lock said inserts in place, and said skirt having diametrically opposed shoulders between said recessed portions and said annular ring area to prevent said inserts from moving toward said annular ring area during reciprocation of said piston.

3. A cast piston for an internal combustion engine having an aluminum body with an annular ring area and a cylindrical skirt depending therefrom, said skirt having diametrically opposed wrist pin supporting bosses with aligned pin holes therein, said skirt having diametrically opposed wear areas substantially normal to the axis of said wrist pin bosses, said skirt having an exterior recessed portion in each of said wear areas, a semi-porous, arcuate, ferrous mteal insert received within each of said recessed portions, said inserts being cast integrally with said piston and having their longitudinal edges flared inwardly throughout their entire length, said inwardly flared longitudinal edges having a plurality of apertures throughout their length to receive metal from said piston as said piston is cast to lock said inserts in place, and said skirt having two pairs of diametrically opposed shoulders which define the tops and bottoms of said recesses to prevent said inserts from moving toward or away from said ring area during reciprocation of said piston.

References Cited in the file of this patent UNITED STATES PATENTS 1,347,480 .leffries July 20, 1920 1,707,748 Wood Apr. 2, 1929 2,026,611 Chase Jan. 7, 1936 2,080,286 Mable May 11, 1937 

